Changes In Species Composition Research Articles

The dynamism fish‐plant association: Ontogenetic variations in assemblage attributes in neotropical floodplain lakes

AbstractStructural habitat complexity provided by macrophytes is expected to increase richness and abundance of fish species. However, this topic is rarely investigated simultaneously at different periods of fish development. We sampled fish within macrophyte stands and in non‐vegetated areas at floodplain lakes and tested the hypothesis that the presence of macrophytes increases abundance and species richness of fish, in addition to changes in species composition, at different periods of fish development. Our findings demonstrated that, in different period of fish development, the highest values of fish species richness and abundance were found at sites colonised by macrophytes. Similarly, changes in fish species composition were observed between habitats colonised by macrophytes and non‐vegetated areas. Therefore, the results demonstrate that macrophyte presence plays an important role in regulating fish community structure at different periods of fish development.

Understory plant communities show resistance to drought, hurricanes, and experimental warming in a wet tropical forest

Global climate change has led to rising temperatures and to more frequent and intense climatic events, such as storms and droughts. Changes in climate and disturbance regimes can have non-additive effects on plant communities and result in complicated legacies we have yet to understand. This is especially true for tropical forests, which play a significant role in regulating global climate. We used understory vegetation data from the Tropical Responses to Altered Climate Experiment (TRACE) in Puerto Rico to evaluate how plant communities responded to climate warming and disturbance. The TRACE understory vegetation was exposed to a severe drought (2015), 2 years of experimental warming (4°C above ambient in half of the plots, 2016–2017 and 2018–2019), and two major hurricanes (Irma and María, September 2017). Woody seedlings and saplings were censused yearly from 2015 to 2019, with an additional census in 2015 after the drought ended. We evaluated disturbance-driven changes in species richness, diversity, and composition across ontogeny. We then used Bayesian predictive trait modeling to assess how species responded to disturbance and how this might influence the functional structure of the plant community. Our results show decreased seedling richness after hurricane disturbance, as well as increased sapling richness and diversity after warming. We found a shift in species composition through time for both seedlings and saplings, yet the individual effects of each disturbance were not significant. At both ontogenetic stages, we observed about twice as many species responding to experimental warming as those responding to drought and hurricanes. Predicted changes in functional structure point to disturbance-driven functional shifts toward a mixture of fast-growing and drought-tolerant species. Our findings demonstrate that the tropical forest understory community is more resistant to climatic stressors than expected, especially at the sapling stage. However, early signs of changes in species composition suggest that, in a warming climate with frequent droughts and hurricanes, plant communities might shift over time toward fast-growing or drought-tolerant species.

Forest tree species distribution for Europe 2000-2020: mapping potential and realized distributions using spatiotemporal machine learning.

This article describes a data-driven framework based on spatiotemporal machine learning to produce distribution maps for 16 tree species (Abies alba Mill., Castanea sativa Mill., Corylus avellana L., Fagus sylvatica L., Olea europaea L., Picea abies L. H. Karst., Pinus halepensis Mill., Pinus nigra J. F. Arnold, Pinus pinea L., Pinus sylvestris L., Prunus avium L., Quercus cerris L., Quercus ilex L., Quercus robur L., Quercus suber L. and Salix caprea L.) at high spatial resolution (30 m). Tree occurrence data for a total of three million of points was used to train different algorithms: random forest, gradient-boosted trees, generalized linear models, k-nearest neighbors, CART and an artificial neural network. A stack of 305 coarse and high resolution covariates representing spectral reflectance, different biophysical conditions and biotic competition was used as predictors for realized distributions, while potential distribution was modelled with environmental predictors only. Logloss and computing time were used to select the three best algorithms to tune and train an ensemble model based on stacking with a logistic regressor as a meta-learner. An ensemble model was trained for each species: probability and model uncertainty maps of realized distribution were produced for each species using a time window of 4 years for a total of six distribution maps per species, while for potential distributions only one map per species was produced. Results of spatial cross validation show that the ensemble model consistently outperformed or performed as good as the best individual model in both potential and realized distribution tasks, with potential distribution models achieving higher predictive performances (TSS = 0.898, R2logloss = 0.857) than realized distribution ones on average (TSS = 0.874, R2logloss = 0.839). Ensemble models for Q. suber achieved the best performances in both potential (TSS = 0.968, R2logloss = 0.952) and realized (TSS = 0.959, R2logloss = 0.949) distribution, while P. sylvestris (TSS = 0.731, 0.785, R2logloss = 0.585, 0.670, respectively, for potential and realized distribution) and P. nigra (TSS = 0.658, 0.686, R2logloss = 0.623, 0.664) achieved the worst. Importance of predictor variables differed across species and models, with the green band for summer and the Normalized Difference Vegetation Index (NDVI) for fall for realized distribution and the diffuse irradiation and precipitation of the driest quarter (BIO17) being the most frequent and important for potential distribution. On average, fine-resolution models outperformed coarse resolution models (250 m) for realized distribution (TSS = +6.5%, R2logloss = +7.5%). The framework shows how combining continuous and consistent Earth Observation time series data with state of the art machine learning can be used to derive dynamic distribution maps. The produced predictions can be used to quantify temporal trends of potential forest degradation and species composition change.

Species composition and identification of pathogens of real powdery mildew of pumpkin crops

When cultivating pumpkin crops in most agricultural regions of the world, one of the most aggressive diseases is real powdery mildew, the damage of plants in which, under optimal soil and climatic conditions for the pathogen, reaches 100%. In the open and protected ground, among the cultivated representatives of the Cucurbitaceae family, the most widespread and harmful are the species Sphaerotheca fuliginea (Schlecht ex Fr.) Poll and Erysiphe cichoracearum f. sp. cucurbitacearum (DC ex Merat). In regions where both phytopathogens are present, mixed infections may occur, making identification difficult, and, accordingly, further plant protection measures. The pathogens of this powdery mildew of pumpkin crops have different requirements for temperature and humidity. During the growing season, there may be a change in species composition when conditions change, for example, when a new season begins. Symptoms of the disease in the form of a white or yellowish powdery plaque in the form of rounded spots (mainly on the leaves) can manifest themselves at all stages of plant development, the susceptibility of which increases by the beginning of fruiting. According to biological characteristics, S. fuliginea and E. cichoracearum are obligate biotrophic pathogens, unable to exist independently without living photosynthetic tissue, except for the wintering (sexual) stage of teleomorphs in the form of globular kleistothecia. At this stage, it is not difficult to differentiate pathogens by the morphology of kleistothecium. When analyzing the plant material of melons with the naked eye, S. fuliginea and E. cichoracearum cause similar symptoms of damage, but by microscopy these organisms can be distinguished by a complex of morphological characteristics. Taxonomically significant features are: the location of the mycelium, the formation of conidia (single or chain), the presence or absence of noticeable fibrosin bodies, the features of the appressoria, the size and shape of the conidia, as well as the position and type of their sprout tubes. The works of Russian and foreign scientists have shown the possibility of determining the types and physiological races of pathogens using an indirect method: reactions to differentiator plants. To date, about 30 physiological races of the pathogen Podosphaera xanthii (Sphaerotheca fuliginea) and 2 races of E. cichoracearum are known. However, this method does not always correlate with the methods of molecular analysis. Determination of the species composition of powdery mildew pathogens is a starting point for the development of a further strategy for the cultivation of pumpkin crops and in breeding work for resistance to this disease.

Importance of climate‐induced tree species composition changes in forecasting the amount of reachable habitat for forest birds

AbstractAimBird and tree species distributions will shift along with future climatic conditions through direct effects related to species responses to bioclimatic variables. In addition, tree species composition changes should indirectly drive changes in forest bird habitats. Here, we predicted the effects of climate changes on the amount of reachable habitat for forest birds and teased apart the role of the indirect effects.LocationFrance.MethodsWe projected tree and bird species distributions (2020 and 2050) using generalized additive models which accounted for climatic conditions at a large scale (France) and local environmental conditions at regional scale. The projections combined two scenarios of climate changes (RCP 2.6 and 8.5) and two scenarios of forest management (increase in either deciduous or coniferous stands). We modelled the amount of reachable habitat with landscape graphs and the equivalent connectivity index (EC) for five birds associated to the main forest types of the study area. To differentiate the sources of EC change between 2020 and 2050, we compared two future landscape graphs including only the indirect effect, or the direct and indirect effects of climate changes.ResultsFor birds with low and intermediate thermal maxima, climate‐based distributions were nearly stable over time (absence of direct effects), EC change was only attributed to indirect effects. In contrast, for bird species with high thermal maximum, EC change was mostly driven by direct effects (more favourable climatic conditions) and little by indirect effects.Main conclusionsUsing an innovative modelling framework that bind species distribution and connectivity models with climate and land use changes in forest, we showed that EC dynamics could be completely due to climate‐driven changes in tree species composition. Our results highlight the importance of accounting for the indirect effects of climate changes, especially in forests where major shifts in tree species composition are expected.

Mesozooplankton composition and distribution in İzmir Bay, Aegean Sea: With special emphasis on copepods

Mesozooplankton are a diverse group of heterotrophic organisms and an important component of the food web in transferring energy to higher trophic levels. Studies on mesozooplankton composition and distribution in İzmir Bay, Aegean Sea, are scarce and they included mostly the data from early 2000s. The present study provides updated information on the status of this important component of the bay. Mesozooplankton composition and distribution were studied in June and November 2017, February and April 2018 from eight stations situated along a transit from inner to the outer region in İzmir Bay, Aegean Sea. Samples were collected vertically by using WP2 net with 200μm mesh size. The total mesozooplankton abundance varied from 708 ind. m−3 in June to 42045 ind. m−3 in April. The high abundance of polychaeta larvae, cirriped nauplii, copepods and appendicularians were observed in the inner region, while the abundance of echinoderm larvae, chaetognaths, siphonophores and pteropods were high in the central and outer regions. The contribution of copepod to the total mesozooplankton abundance was the highest (≥ 56 %) in February in all regions. The lowest contributions were in November (32 %) in the inner region and in June in the central (27 %) and the outer (29 %) regions. A total of 38 copepod species were identified during the study period. Acartia clausi successively dominated the copepod community in February and April. Oithona nana was the most abundant oithonid in February and April, while O. davisae in November. O. similis, Paracalanus parvus, Oncaea media group, Temora stylifera and Centropages typicus were abundant in the central and outer regions of the bay. Four new species, Parvocalanus crassirostris, Pseudodiaptomus marinus, Centropages ponticus and Oithona tenuis were detected for the first time in the bay. The reported abundance of C. ponticus, P. crassirostris and P. marinus, together with their spatial and temporal occurrence in the present study, indicate that these species have already settled in İzmir Bay. Results indicate that the mesozooplankton distribution and composition were associated mostly with salinity and depth rather than temperature in group and species level. Substantial changes in the copepod species composition have been observed over decades in İzmir Bay. The number and abundance of smaller and egg-sac carrying non-indigenous species appear to be increasing over time in the bay.

A suggested climate service for cyanobacteria blooms in the Baltic Sea – Comparing three monitoring methods

Dense blooms of filamentous cyanobacteria are recurrent phenomena in the Baltic Sea, with occasional negative effects on the surrounding ecosystem, as well as on tourism, human health, aquaculture, and fisheries. Establishing a climate service is therefore suggested; including multi-method observations of cyanobacteria biomass, biodiversity, and biogeography, in correspondence to biotic and abiotic factors. Three different approaches were compared for determination of spatial and temporal variability and trends of the blooms; 1) microscopy-based long-term data, 2) satellite remote sensing, and 3) phycocyanin fluorescence mounted on a merchant vessel. Firstly, microscopy-based data on cyanobacteria biomass from the period 2000–2020 showed that the toxin producing genus Nodularia and non-toxic Aphanizomenon both had summer means of 15 µg C L−1, while Dolichospermum was less dominant with a mean of 8 µg C L−1. Some years also the Kattegat was affected by cyanobacteria blooms, likely transported here by ocean currents. Secondly, the satellite remote sensing time series for the period 2002–2020 indicated that near surface blooms were most frequent in the Northern Baltic Proper and that near surface blooms have increased in the Bothnian Sea, starting later in the season than in the Baltic Proper. The largest extents (i.e., total area covered) were observed in 2005, 2008, and 2018. Thirdly, phycocyanin fluorescence from a flow through sensor mounted on a merchant vessel was used as a proxy for cyanobacteria biomass and correlated to cyanobacteria biomass estimated by microscopy. However, the satellite remote sensing data on surface accumulations showed little resemblance to the data on cyanobacteria biomass based on water sampling and microscopy, interpreted as an effect of methods. Sensors on satellites mainly detect surface accumulations of cyanobacteria while the microscopy data was based on samples 0–10 m, thereby comprising a larger community. Data from satellite remote sensing of cyanobacteria was correlated to the phycocyanin fluorescence indicating that similar bio-optical properties are observed. Finally, results from a downscaled ocean climate model (NEMONordic) were used to produce future scenarios for temperature and salinity, which directly affects cyanobacteria blooms in the Baltic Sea, supposedly by increasing in abundance and change in species composition. Short-term forecasts can be used together with observations for early warning of cyanobacteria blooms, and we suggest an internationally coordinated cyanobacteria observation and warning system for the Baltic Sea area.

Lessons from a next generation carbon ranching experiment

Identifying grazing practices that maximize food production and soil carbon sequestration is of global importance. Currently, we cannot reliably predict which grazing practice will accrue the most soil organic carbon (SOC) partly because of confusion created by an abundance of low-quality experiments. Data quality has likely suffered because adequate treatment replication requires a lot of land, meaningful scale introduces heterogeneity among replicates, and pre-existing differences are often not taken into account. Here we tested the effects of five grazing treatments on SOC stocks with a gold standard randomized controlled trial (RCT) with pre-treatment data. Treatments were no grazing, severe summer grazing, moderate fall grazing, severe fall grazing, and the conventional approach for the system of moderate summer grazing. Because grazing experiments are often little-replicated, we also gauged the dependence of results on pre-treatment data by comparing the results of analyses with vs without pre-treatment data. We also tested for relationships between plant (root biomass, plant species composition) and soil properties (mass, nitrogen concentration) and SOC. After applying treatments for 5-yr, the no grazing and severe summer and fall grazing treatments accrued 0.85 to 1.22 kg × m−2 (0–60 cm soil depth) more SOC than conventional moderate summer grazing and represent appreciable (i.e. >4 per mille per yr) increases in SOC stocks. Furthermore, the entire portfolio of new grazing practices increased SOC accrual compared to conventional management. Given the divergent characteristics of the newly applied practices, sustainable accrual of SOC may depend on management heterogeneity. Accrual of SOC was likely driven by a reduction in SOC mineralization related to increased soil density and nitrogen, decreased root biomass, and change in plant species composition. Our findings counter the prevailing view that plant material inputs are the primary driver of SOC accrual in grazing lands. In other words, SOC accrual was mainly associated with indicators of decreased SOC mineralization (C outputs). We also found unique results for analyses with and without pre-treatment data, thereby indicating the risk of unreliable results for little-replicated RCTs without pre-treatment data. Robust generalizations on grazing practices that will reliably and sustainably maximize the rate of SOC accrual for a specific system, climate and timeline are still lacking, but further focus on factors affecting SOC mineralization will facilitate their development.

Livestock Grazing Impact on Species Composition and Richness Understory of the Pinus cembroides Zucc. Forest in Northeastern Mexico

In the pine forests of Mexico, disturbances are primarily due to cattle, horses, goat, and sheep grazing, particularly in communal grazing lands. The most evident disturbances are low tree recruitment, invasive shrubs establishment, species composition changes, and invasion of weeds dispersed mainly by livestock. The Sierra de Zapalinamé is a mountain range and natural protected area of northeast Mexico. We conducted the current study in this area in a forest stand of Pinus cembroides excluded from grazing in the last 25 years (1200 ha with pine forest vegetation and mountain chaparral) and another area nearby subjected to livestock grazing. Forest structure (basal area and density), tree species richness, total understory species richness, and understory species composition were analyzed at the control and grazed sites. Our results revealed that grazing has modified the understory species composition and reduced the evenness in the control plots. Therefore, to maintain species diversity and forest structure, we concluded that extensive grazing should be restricted for some areas or the number of animals reduced in zones of high ecological value.

Marine Benthic Algal Composition after 45 Years in an Urbanized Bay in Cebu, Philippines

Coastal ecosystems have been seriously impacted by anthropogenic activities, which are compounded by recent climatic and environmental changes. To provide some evidence of these changes, a study of marine benthic algal composition was conducted by comparing historical (1969–1970) and contemporary (2013–2014) collections in Silot Bay in Cebu, Philippines. A quantitative survey revealed a total of 30 species of benthic algae (11 red, nine brown, and 10 green) in the historical collections, whereas only 15 species (four each of red and brown plus seven species of green algae) were accounted in the latter years. This decline in the marine benthic algal composition may be attributed to sedimentation, which is indirectly caused by urbanization and human population increase. Altered environmental conditions inside the Bay may also explain the decline and qualitative changes of algal species composition therein. Continued monitoring of the benthic macroalgal composition and environmental parameters may help document anthropogenic impacts on marine ecosystems. Historical herbarium samples represent a valuable yet underappreciated resource for tracking environmental changes through time.

Forest density and edge effects on soil microbial communities in deciduous forests across Europe

Forest fragmentation increases the proportion of edge area and this, in turn, induces changes in forest structure, species composition and microclimate. These factors are also strongly determined by the forest management regime. Although the interactive effects of edges and density on forest plant communities have been extensively studied, little is known about the response of the belowground communities. Here we investigated the variation of soil microbiota in 45 deciduous broadleaved forests along a latitudinal gradient from Italy to Norway at a continental scale across Europe. Phospholipid fatty acid (PLFA) and neutral lipid fatty acid (NLFA) were used to map the microbial community in the forest edge and interior across three forest densities (dense, intermediate, open forest). Microbial community composition was only affected by forest edge effects and not by forest density. We did not find any interaction effects between forest density and distance-to-edge. Arbuscular mycorrhizal fungi (AMF) were significantly more abundant in edges and Gram-negative bacteria more abundant in interiors, respectively. The microbial community composition was closely related to soil pH, soil potassium and nitrogen, texture (percent sand) and soil temperature. Soil pH was positively correlated with the saprotrophic fungi and potassium was positively correlated with Gram-negative bacteria but negatively correlated with Actinobacteria. In sum, we reveal the notable effects of forest edges on the soil AMF abundance. This result indicated that AMF could possess a stronger affinity with species growing in the edges, which may help to improve plant performance under hostile conditions herein.

Summer grazing by three livestock species at moderate intensity enhances primary productivity and drives community divergence in a semi‐arid steppe

AbstractAimsThe general effects of grazing by large herbivores on plant species composition and productivity are well known. Meanwhile, how different livestock species affect community structure is not fully understood. In northern China, livestock species composition is changing rapidly and hence, it is imperative to understand the resulting effects on grassland productivity and composition.LocationXilingol, Inner Mongolia, China.MethodsWe studied how grazing by three major livestock species affects typical steppe dominated by Leymus chinensis, Stipa grandis, Cleistogenes squarrosa and Carex korshinskyi, in a 4‐year field experiment using a random block‐design with four treatments (sheep, goat, cattle, no grazing), under summer grazing at moderate intensity. We calculated above‐ground net primary productivity (ANPP) and a selectivity index (SI) based on biomass to quantify livestock forage preferences.ResultWe found that (i) sheep preferred Leymus chinensis and mixed subordinate species, cattle preferred Stipa grandis, and goat preferred Carex korshinskyi and Cleistogenes squarrosa. (ii) Consistent with these preferences, sheep increased the relative biomass of Stipa grandis, but reduced that of Carex korshinskyi; cattle reduced the relative biomass of Stipa grandis and Carex korshinskyi but increased that of mixed subordinate species; and goats reduced the relative biomass of Cleistogenes squarrosa and Carex korshinskyi but increased that of mixed subordinate species. (iii) Overall, grazing significantly increased ANPP, mainly due to an increase in ANPP of Leymus chinensis and subordinate species, at the cost of Stipa grandis.ConclusionsSummer grazing by different livestock species at moderate intensity can increase ANPP, while livestock forage preferences can drive divergent changes in species composition. Our results also imply that livestock composition can be used as a mean to manage vegetation dynamics.

Changes in tree layer and altitudinal distribution of herbaceous species in temperate old-growth forests over 30 years

Temperate forest ecosystems, including old-growth fragments, are subject to increasing pressures, both from biotic and abiotic factors. Frequent disturbance events, rising mean annual temperatures and longer-lasting droughts are causing changes in tree species composition, probably shifting the altitudinal distribution of herbaceous species as well. Our goal was to examine whether such shifts can be observed even in old-growth temperate forests, and if the changes in the species composition and spatial distribution of trees is reflected in the herbaceous layer. Our study was based on a survey of several old-growth forests from the 1970s that was repeated after 30 years. Using spatial point pattern methods and generalized linear mixed effect models, repeated measurements of mapped phytosociological relevés and detailed maps of tree positions from two survey periods allowed us to examine how the species composition of the herb layer and the spatial distribution of trees ≥ 10 cm DBH (diameter at breast height) changed over 30 years. On most of the studied sites, the total number of trees declined and the proportion of broadleaves increased between the two surveys. Analyses of tree spatial distribution showed a general shift from a regular spatial distribution in the 1970s to a clustered spatial distribution of trees in the 2000s. In the 2000s, herbaceous species showed an upwards shift in their distribution compared to the 1970s, even after accounting for the effect of changing tree spatial distributions in both survey periods. These effects could be an outcome of warmer and drier weather conditions during the past decades. Further investigation is needed to examine whether this trend is related to changes in climatic conditions.

변산반도국립공원 꽝꽝나무군락의 생태적 특성

In order to preserve and restore the habitats of Ilex crenata community distributed in Byeonsanbando National Park, the ecological characteristics of flora and major vegetation were investigated centered on the community distribution area. A total of 36 taxa with 22 families, 21 genera, 32 species, and 4 variants, were investigated in the vicinity of the Ilex crenata community. At close distances centered on the area around the Ilex crenata community, the vegetation was found to be a mountain coniferous forest called Pinus densiflora-Quercus serrata community(35° 39′ 18.62″ north latitude, 126° 34′ 56.70 east longitude), at an elevation of 85m to 95m above sea level, an inclination of 10° to 15°, and clustered around the south and southwest slopes. In the Tree-1 layer, there are Pinus densiflora, Quercus serrata, Quercus variabilis, and Prunus serrulata var. pubescens. In the Tree-2 layer, there are Quercus serrata, Quercus variabilis, Prunus serrulata var. pubescens, Styrax japonicus, and Acer pseudo-sieboldianum. In the Shrub layer, there are Ilex crenata, Rhododendron mucronulatum, Lespedeza maximowiczii, Fraxinus sieboldiana, Smilax china, Lindera obtusiloba, Fraxinus rhynchophylla, Rhododendron schlippenbachii, Lindera glauca, Juniperus rigida var. rigida. In the past, before the Buam Dam was built, the surrounding area was a rice paddy field and farmland, but after the Buam Dam was completed, due to changes in the climatic environment, such as fog and humidity, which occurred around the Buan Dam, It is predicted that changes in species composition within the community will appear as the blooming of Quercus serrata increases in the Tree-1 layer and Tree-2 layer, as Fraxinus sieboldiana, Fraxinus rhynchophylla, Lindera obtusiloba, etc. appear in the shrub layer, and Sasa borealis Indigofera kirilowii, Carex lanceolata, and Fraxinus sieboldiana, etc. appear in the herb layer. The distribution area of Ilex crenata community was measured to be 384㎡, the height of Ilex crenata was in the range of 2.2 to 2.5m, and the diameter of the rhizome of Ilex crenata community was Ø48.5mm+39.4mm+46.9mm+37.3mm, It is considered to be in good growth condition due to the stable management and protection of the colony area. In addition, as it is expected that Ilex crenata community will gradually spread as a constituent species of the shrub layer and the herbaceous layer in the pine and Ilex crenata community communities near the native habitats of the black oak community, a detailed investigation into these areas and monitoring for continuous conservation and restoration are needed in the future.

The health condition of trees in dendropark at Faculty of Forestry – Skopje with a special focus on fungal diseases and insect pests

The Dendropark at the Faculty of Forestry in Skopje, North Macedonia, was established as an ‘outdoor museum’ with a collection of forest trees and shrub vegetation. The collection was planted in 1950 on the area of 4.05 ha, and includes 336 taxa from native Macedonian and Balkan endemic dendroflora and introduced species from around the world. The Dendropark, like the other botanical gardens all over the world, offers a unique resource that facilitate earlier detection of the potential invasive threats to forest tree species. The inventoried population includes 444 trees belonging to 43 families. The three most represented families are Pinaceae with 21 species (19.4% of the inventoried plants), Cupressaceae with 16 species (15.8%) and Rosaceae with 18 species (7.4%). The 2014 survey indicated that 33.8% of the total number of trees were rated with good health status, 1.8% as very good, 31.1% rated as fair, while 24.5% were poor. Approximately 4.1% were rated to be in a critical state (in a state of decline), and 4.7% of trees were dead. The assessment of health status of plants in the Dendropark could be used as a valuable asset to planners and decision makers and provides information about the quality, quantity and location of natural resources in urban areas. Identifying changes in plant species composition and presence of invasive pests and diseases helps maintaining healthy urban forests.

Differential nutrient limitation and tree height control leaf physiology, supporting niche partitioning in tropical dipterocarp forests

Abstract Revealing the mechanisms of environmental niche partitioning within lowland tropical forests is important for understanding the drivers of current species distributions and potential vulnerability to environmental change. Tropical forest structure and species composition change across edaphic gradients in Borneo over short distances. However, our understanding of how edaphic conditions affect tree physiology and whether these relationships drive niche partitioning within Bornean forests remains incomplete. This study evaluated how leaf physiological function changes with nutrient availability across a fine‐scale edaphic gradient and whether these relationships vary according to tree height. Furthermore, we tested whether intraspecific leaf trait variation allows generalist species to populate a wider range of environments. We measured leaf traits of 218 trees ranging in height from 4 to 66 m from 13 dipterocarp species within four tropical forest types (alluvial, mudstone, sandstone and kerangas) occurring along an <5 km edaphic gradient in North Borneo. The traits measured included saturating photosynthesis (Asat), maximum photosynthetic capacity (Vcmax), leaf dark respiration (Rleaf), leaf mass per area (LMA), leaf thickness, minimum stomatal conductance (gdark) and leaf nutrient concentrations (N, P, Ca, K and Mg). Across all species, leaf traits varied consistently in response to soil nutrient availability across forest types except Rleaf_mass, [Mg]leaf and [Ca]leaf. Changes in photosynthesis and respiration rates were related to different leaf nutrients across forest types, with greater nutrient‐use efficiency in more nutrient‐poor environments. Generalist species partially or fully compensated reductions in mass‐based photosynthesis through increasing LMA in more nutrient‐poor environments. Leaf traits also varied with tree height, except Vcmax_mass, but only in response to height‐related modifications of leaf morphology (LMA and leaf thickness). These height–trait relationships did not vary across the edaphic gradient, except for Asat, [N]leaf, [P]leaf and [K]leaf. Our results highlight that modification of leaf physiological function and morphology act as important adaptations for Bornean dipterocarps in response to edaphic and vertical environmental gradients. Meanwhile, multiple nutrients appear to contribute to niche partitioning and could drive species distributions and high biodiversity within Bornean forest landscapes. Read the free Plain Language Summary for this article on the Journal blog.

Preliminary patterns of seasonal changes in species composition of surface‐active arthropods in a South African savannah

AbstractSurface‐active arthropods have limited dispersal abilities and their abundances are responsive to changes in the environment. Their sensitivity allows for the identification of aspects of environmental variation that are responsible for changes in community assemblages of these arthropods. Limited dispersal abilities allow for changes in the populations of surface‐active arthropods to be linked reliably to changes in their local environment. In this study, we tested the hypothesis that seasonal variation in resource availability drives assemblages of three groups of surface‐active arthropods (ants, beetles and spiders). Ten study sites were selected, where sampling was carried out continually during the wet, austral summer season (December 2018–February 2019) and then repeated at the same sites in the dry winter season (June 2019–August 2019) in a mesic savannah of Mpumalanga province, South Africa. Pitfall trapping was used to sample the surface‐active arthropods. We found 89 morphospecies of ants, 48% of which were members of the Myrmicinae, while 32% of the 163 morphospecies of beetles were the Scarabaeidae. There were 262 morphospecies of spiders, of these, 22% were from the Salticidae. We found similar abundance and species richness of ants between seasons but significantly greater abundance and species richness of beetles and spiders in summer than in winter. These results show that the impact of seasonal variation in resource availability differs among arthropod taxa. However, the species compositions of all three taxa were significantly different between summer and winter. These results can be explained by the ‘niche differentiation hypothesis’ coupled with the ‘resource‐ratio hypothesis’. Additionally, these results highlight the role that temporal and dietary niche differentiation play in driving the assemblage composition of surface‐active arthropods in a mesic savannah.

Tree stratum alteration decreases C use efficiency and the stability of litter decomposition in a sacred fir ( Abies religiosa ) forest

Background: There is limited information to predict the direction in which canopy modification affects the microbial carbon use efficiency (CUE) and, consequently, the magnitude and stability of litter decomposition in monodominant sacred fir ( Abies religiosa ) forests.
 Questions: What is the effect of tree stratum alteration on CUE and stability of litter decomposition in an A. religiosa forest?
 Study sites and dates: Two conditions inside a sacred fir forest were selected: A) a naturally monodominant homogeneous condition, and B) a heterogeneous condition with a non-monospecific tree stratum derived from local disturbances (wildfire and reforestation) occurred on a single occasion 18 years ago.
 Methods: In each condition (homogeneous and heterogeneous), the Importance Value Index (IVI) was calculated in the tree stratum, while chemical composition, microbial carbon (C) concentration, enzyme activities and C mineralization were measured in litter samples. The specific enzymatic activity and the metabolic quotient were calculated as CUE indicators, and the coefficient of variation as a proxy for litter decomposition stability.
 Results: A change in tree species composition and an increase in tree species richness in the heterogeneous condition was found, which decreased litter phosphorous (P) concentration. This promoted a high microbial activity and low CUE, favoring C mineralization. Furthermore, low stability during litter decomposition was observed as tree species richness increased.
 Conclusions: Tree stratum heterogeneity, as a consequence of past disturbances, decreases CUE and the stability of litter decomposition in an A. religiosa forest.

Upslope release—Downslope receipt? Multi‐year plant uptake of permafrost‐released nitrogen along an arctic hillslope

Abstract As arctic permafrost continues to thaw, previously inaccessible nitrogen (N) becomes available to N‐limited arctic plants. Increased N availability could enhance plant growth and thereby potentially offset climate‐induced carbon release. Arctic plants can take up newly available permafrost‐N locally upon release. However, in a topographically diverse arctic landscape, permafrost‐N may be transported along hillslopes, away from the point‐of‐release. The extent to which topographical N transport can impact arctic vegetation change depends on whether N is retained locally, captured by downslope recipient plant communities, or transported away. We used stable isotope labelling (15N) to simulate upslope release of ammonium (NH4+) and nitrate (NO3−) from thawing permafrost on an arctic hillslope, western Greenland. We tracked the plant species‐specific uptake of simulated permafrost‐released N from the upslope point‐of‐release to the bottom of the slope through 4 years. We found that arctic tundra plants successfully acquired locally released permafrost‐N, even in sloping terrain, and that N was strongly retained in the plant–soil system through multiple years. At the same time, we also importantly demonstrate that permafrost‐N can be transported and taken up by plants up to 30 m downslope from the point‐of‐release. Especially NO3− was more easily redistributed vertically within the soil column compared to NH4+ and therefore potentially more accessible to plants. Specifically, plant species with fast N uptake capacity and deep‐soil foraging strategies may have competitive advantages for capitalising on deep‐soil released and topographically transported permafrost‐N (here exemplified by Equisetum arvense and Salix glauca). Nevertheless, even mosses gained access to permafrost‐N via vertical and lateral redistribution on the slope. Ultimately, the intricate balance between strong local N retention, downslope transport and plant species‐specific uptake strategies may contribute to shaping arctic vegetation change. Synthesis. Across spatially complex arctic ecosystems, arctic plants can take up permafrost‐released N both at the local point‐of‐release and at a considerable distance downslope. The potential for arctic plants to take advantage of topographically transported permafrost‐N could lead to long‐term and landscape‐scale changes in species composition, plant productivity, and ultimately carbon and climate feedbacks across the Arctic.

Fish Species Diversity From Someșul Cald River: 50Years After Cascade Dam Constructions

In the present study, changes in fish species composition, distribution, and diversity caused by cascade dam constructions on Someșul Cald River, Romania, were analyzed. Cascade dam constructions may act as a freshwater stressor both on short and long term. The river was divided into two sections according to the positioning of the cascade dams (T1-inferior section, respectively T2-superior section). In the T1 and T2 sections, 8 and 12 sampling stations were established, respectively. A total number of 1789 specimens grouped in 12 species and 8 families were sampled from August to September 2018. The most abundant species in both sections was S. trutta. The most abundant family was Salmonidae, with 66.2%. Alpha diversity (species richness) in the T2 section was higher than in T1 (T2 = 12 species vs T1 = 9 species). The Kruskal-Wallis test indicated no significant differences (p > 0.05) for beta diversity of T1 vs T2 (Sørensen coefficient). The species that contributed most to the dissimilarities between the two river sections were T. thymallus, B. carpathicus, C. gobio, and S. cephalus, their summed contribution to the dissimilarity being larger than 50%. The analyzed environmental variables influenced the distribution of some fish species. Alpha and beta diversity distribution on elevation gradient showed that stations close to reservoirs had more species (both in T1 and T2 sections) than the other stations, clearly showing that the distance from lake/reservoir is influencing species richness. The effect of dams from Someșul Cald River on fish species distribution was analyzed by comparing previous data (before 1968) to recent collected data.